• Korean Journal of Materials Research
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• v.27 no.6
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• pp.331-338
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• 2017

This study was carried out to investigate the optimum condition of a friction stir welding process for a joint of AA2219-T87 and AA2195-T8 dissimilar aluminum alloys. These alloys are known to have good cryogenic properties, and as such to be suitable for use in fuel tanks of space vehicles. The welding parameters include the travelling speed, rotation speed and rotation direction of the tool. The experiment was conducted under conditions in which the travelling speed of the tool was 120-300 mm/min and the rotation speed of the tool was 400-800 rpm. To investigate the effect of the rotation direction of the tool, the joining was performed by switching the positions of the two dissimilar alloys. After welding, the microstructure was observed and the micro-hardness were measured; non-destructive evaluation was carried out to perform tensile tests on defect-free specimens. The result was that the microstructure of the weld joint underwent dynamic recrystallization due to sufficient deformation and frictional heat. The travelling speed of the tool had little effect on the properties of the joint, but the properties of the joint varied with the rotation speed of the tool. The conditions for the best joining properties were 600 rpm and 180-240 mm/min when the AA2219-T8 alloy was on the retreating side(RS).

• Tribology and Lubricants
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• v.32 no.3
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• pp.95-100
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• 2016

As an alternative fuel, biodiesel has excellent lubricating property. Previously, our research group reported that the properties of biodiesels depended on their composed molecular structure. In this study, we investigate lubricity and the mechanism of lubricity improvement of synthesized biodiesel molecules. We synthesize four types of biodiesel components from fatty acid via fisher esterification and soybean biodiesel from soybean oil via transesterification in high yield (92-96%). We analyze the lubricity of the five 5 types of biodiesel using HFRR (high frequency reciprocating rig). We estimate that the mechanism of lubricity is relevant to the molecular structure and structure conversion of biodiesel. The test results indicate that the longer the length of molecules and the higher the content of olefin, the better the lubricity of the biodiesel molecules. However, the wear scar size of the first test samples’ do not show a regular pattern with the wear scar size of the second test samples’. Moreover, we investigated the structure conversion of the biodiesels by using GC-MS for the recovered biodiesel samples from the HFRR test. However, we do not detect structure conversion. Thus, we conclude that the lubricity of biodiesel depends on how effectively solid adsorption and boundary lubrication occurs based on the size of the molecule and the content of olefin in the molecule. In addition, HFRR test condition in not sufficient for Diels-Alder cyclization of biodiesel components.

• Tribology and Lubricants
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• v.35 no.5
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• pp.267-273
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• 2019

Wheel bearings are important automotive parts that bear the vehicle weight and translate rotation motion; in addition, their seals are components that prevent grease leakage and foreign material from entering from the outside of the bearings. Recently, as the need for electric vehicles and eco-friendly vehicles has been emerging, the reduction in fuel consumption and $CO_2$ emissions are becoming the most important issues for automobile manufacturers. In the case of wheel bearings, seals are a key part of drag torque. In this study, we investigate the prediction of the drag torque taking into consideration the hyperelastic and viscoelastic material properties of automotive wheel bearing seals. Numerical analysis based on the finite element method is conducted for the deformation analyses of the seals. To improve the reliability of the rubber seal analysis, three types of rubber material properties are considered, and analysis is conducted using the hyperelastic material properties. Viscoelastic material property tests are also conducted. Deformation analysis considering the hyperelastic and viscoelastic material properties is performed, and the effects of the viscoelastic material properties are compared with the results obtained by the consideration of the hyperelastic material properties. As a result of these analyses, the drag torque is 0.29 Nm when the hyperelastic characteristics are taken into account, and the drag torque is 0.27 Nm when both the hyperelastic and viscoelastic characteristics are taken into account. Therefore, it is determined that the analysis considering both hyperelastic and viscoelastic characteristics must be performed because of its reliability in predicting the drag torque of the rubber seals.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.18 no.4
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• pp.509-516
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• 2020

An important property of glass and ceramic solid waste forms is processability. Tellurite materials with low melting temperatures and high halite solubilities have potential as solid waste forms. Crystalline TiTe3O8 was synthesized through a solid-state reaction between stoichiometric amounts of TiO2 and TeO2 powder. The resultant TiTe3O8 crystal had a three-dimensional (3D) structure consisting of TiO6 octahedra and asymmetric TeO4 seesaw moiety groups. The melting temperature of the TiTe3O8 powder was 820℃, and the constituent TeO2 began to evaporate selectively from TiTe3O8 above around 840℃. The leaching rate, as determined using the modified American Society of Testing and Materials static leach test method, of Ti in the TiTe3O8 crystal was less than the order of 10-4 g·m-2·d-1 at 90℃ for durations of 14 d over a pH range of 2-12. The chemical durability of the TiTe3O8 crystal, even under highly acidic and alkaline conditions, was comparable to that of other well-known Ti-based solid waste forms.

• Journal of the Korean Society of Safety
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• v.37 no.2
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• pp.1-9
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• 2022

Most factories deal with toxic or flammable chemicals in their industrial processes. These hazardous substances pose a risk of leakage due to accidents, such as fire and explosion. In the event of chemical release, massive casualties and property damage can result; hence, quantitative risk prediction and assessment are necessary. Several methods are available for evaluating chemical dispersion in the atmosphere, and most analyses are considered neutral in dispersion models and under far-field wind condition. The foregoing assumption renders a model valid only after a considerable time has elapsed from the moment chemicals are released or dispersed from a source. Hence, an initial dispersion model is required to assess risk quantitatively and predict the extent of damage because the most dangerous locations are those near a leak source. In this study, the dispersion model for initial consequence analysis was developed with three-dimensional unsteady advective diffusion equation. In this expression, instantaneous leakage is assumed as a puff, and wind velocity is considered as a coordinate transform in the solution. To minimize the buoyant force, ethane is used as leaked fuel, and two different diffusion coefficients are introduced. The calculated concentration field with a molecular diffusion coefficient shows a moving circular iso-line in the horizontal plane. The maximum concentration decreases as time progresses and distance increases. In the case of using a coefficient for turbulent diffusion, the dispersion along the wind velocity direction is enhanced, and an elliptic iso-contour line is found. The result yielded by a widely used commercial program, ALOHA, was compared with the end point of the lower explosion limit. In the future, we plan to build a more accurate and general initial risk assessment model by considering the turbulence diffusion and buoyancy effect on dispersion.

• Nuclear Engineering and Technology
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• v.53 no.2
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• pp.603-610
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• 2021

The major drawback of zirconia-based materials, in view of their applications as targets for minor actinide transmutation, is their poor thermal conductivity. The addition of MgO, which has high thermal conductivity, to zirconia-based materials is expected to improve their thermal conductivity. On these grounds, the present study aims at phase characterization and thermophysical property evaluation of neodymium-substituted zirconia (Zr_0.8Nd_0.2O_1.9; using Nd₂O₃ as a surrogate for Am₂O₃) and its composites with MgO. The composite was prepared by a solid-state reaction of Zr_0.8Nd_0.2O_1.9 (synthesized by gel combustion) and commercial MgO powders at 1773 K. Phase characterization was carried out by X-ray diffraction and the microstructural investigation was performed using a scanning electron microscope equipped with energy dispersive spectroscopy. The linear thermal expansion coefficient of Zr_0.8Nd_0.2O_1.9 increases upon composite formation with MgO, which is attributed to a higher thermal expansivity of MgO. Similarly, specific heat also increases with the addition of MgO to Zr_0.8Nd_0.2O_1.9. Thermal conductivity was calculated from measured thermal diffusivity, temperature-dependent density and specific heat values. Thermal conductivity of Zr_0.8Nd_0.2O_1.9-MgO (50 wt%) composite is more than that of typical UO₂ fuel, supporting the potential of Zr_0.8Nd_0.2O_1.9-MgO composites as target materials for minor actinides transmutation.

• Structural Engineering and Mechanics
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• v.80 no.6
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• pp.701-709
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• 2021

The paper aims at improving the understanding and mitigating the effects of tunnel fires that may breakout due to the burning fuel and/or explosion within the tunnel. This study particularly focuses on the behavior of the commonly used horse shoe geometry of tunnel systems. The problem has been obtained using an adequate well-established program incorporating the Lagrangian approach. A transient-thermo-coupled static structural analysis is carried out. The effects of radiation and convection to the outer walls of the tunnel is studied. The paper also presents the impact of the hazard on the structural integrity of the tunnel. A methodology is proposed to study the tunnel fire using a model which uses equivalent steel sheet to represent the presence of reinforcements to improve the computational efficiency with adequate validation. A parametric study has been carried out and the effect of suitable lining property for mitigating the fire hazard is arrived at. Detailed analysis is done for the threshold limits of the properties of the lining material to check if it is acceptable in all aspects for the integrity of the tunnel. The study may prove useful for developing insights for ensuring tunnel fire safety. To conduct such studies experimentally are tremendously costly but are required to gain confidence. But, scaled models, as well as loading and testing conditions, cannot be studied by many trials experimentally as the cost will shoot up sharply. In this context, the results obtained from such computational studies with a feasible variation of various combinations of parameters may act as a set of guidelines to freeze the adequate combination of various parameters to conduct one or two costly experiments for confidence building.

• Journal of Practical Agriculture & Fisheries Research
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• v.10 no.1
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• pp.169-181
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• 2008

The purpose of this study was to produce Pleurotus ostreatus using fermenter with bag cultivation. These results are as follows. 1. While mushroom composts were being fermented in a fermenter, the physical property of the fermented composts was getting better when there isn't any screw or revolving flies in the fermenter and the strength of pressing the composts was getting less. 2. The composts were fermented well as slaked lime of 1% density added to the composts. 3. According to the result of examining our fermenting ways, composts were in the best condition after being fermented for 48 hours since the temperature in a fermenter has come to 60℃, which could be reached by heating the fermenter by 40℃ after putting compost materials and water into it. 4. The good condition of fermenting could be maintained by controlling the speed of revolving flies, therefore the speed be down when the temperature is above 60℃ and up bellow 60℃. 5. Since the composts had been added with 1.5~2% of cottonseed meal or rice bran, the fermented composts were in good condition and also the quantity and quality of the mushroom produced on the fermented composts were satisfied. 6. There were needed 7 hours of labour for 3days from the first day of putting composts into a fermenter for fermenting 3.5M/T(10,000~12,000bags of 750~800g per bag) of composts to the third day of finishing the fermenting work, and also the cost was 112,066￦(130$) including 52,066￦(60$) of electric charge and fuel expense.

• Structural Engineering and Mechanics
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• v.87 no.3
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• pp.221-229
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• 2023

Urbanization and industrialization have significantly increased the amount of solid waste produced in recent decades, posing considerable disposal problems and environmental burdens. The practice of waste utilization in concrete has gained popularity among construction practitioners and researchers for the efficient use of resources and the transition to the circular economy in construction. This study employed Lytag aggregate, an environmentally friendly pulverized fuel ash-based lightweight aggregate, as a substitute for natural coarse aggregate. At the same time, fly ash, an industrial by-product, was used as a partial substitute for cement. Concrete mix M20 was experimented with using fly ash and Lytag lightweight aggregate. The percentages of fly ash that make up the replacements were 5%, 10%, 15%, 20%, and 25%. The Compressive Strength (CS), Split Tensile Strength (STS), and deflection were discovered at these percentages after 56 days of testing. The concrete cube, cylinder, and beam specimens were examined in the explorations, as mentioned earlier. The results indicate that a 10% substitution of cement with fly ash and a replacement of coarse aggregate with Lytag lightweight aggregate produced concrete that performed well in terms of mechanical properties and deflection. The cementitious composites have varying characteristics as the environment changes. Therefore, understanding their mechanical properties are crucial for safety reasons. CS, STS, and deflection are the essential property of concrete. Machine learning (ML) approaches have been necessary to predict the CS of concrete. The Artificial Fish Swarm Optimization (AFSO), Particle Swarm Optimization (PSO), and Harmony Search (HS) algorithms were investigated for the prediction of outcomes. This work deftly explains the tremendous AFSO technique, which achieves the precise ideal values of the weights in the model to crown the mathematical modeling technique. This has been proved by the minimum, maximum, and sample median, and the first and third quartiles were used as the basis for a boxplot through the standardized method of showing the dataset. It graphically displays the quantitative value distribution of a field. The correlation matrix and confidence interval were represented graphically using the corrupt method.

• Journal of the Korean Institute of Gas
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• v.28 no.1
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• pp.53-58
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• 2024

Due to the development of industry and improvement of living standards, the amount of natural gas used in the world is constantly increasing, and related industrial facilities such as power plants, storage facilities, and supply pipelines are constantly increasing. Natural gas is a convenient and clean fuel that does not pollute the environment, but in the event of an accident due to leakage, it can cause human casualties, large-scale property damage, and negative effects on the global warming effect. In addition to the severe penalties under the Severe Disaster Punishment Act, it is necessary to ensure safety. Therefore, by applying the principle of laser-based absorption spectroscopy, we developed a long-range portable methane leakage gas detection system that can detect the concentration of methane leaking from a distance of up to 30 meters and verified its effectiveness.